Tax experts have welcomed guidance by the Revenue explaining that individuals working from home can offset some of their mortgage interest against tax.

However, they caution that the latest guidance does not mark any change in the rules but merely confirms what was already the case.

Mike Warburton, senior tax partner at Grant Thornton, the accountant, says: “For a long time it has been the case that self-employed people running a business partly from home could set a proportion of their home running costs against income tax. This could include not only mortgage interest, but also costs such as heating and lighting for the part of the home where business was conducted.

“Accountants should have been aware of this - and so should their clients - but it is always useful to see it set down in black and white by the Revenue.”

Angela Beech, of Blick Rothenberg, another accountant, says that many of those working from home were reluctant to offset home running costs against tax because they feared that they would lose the normal capital gains tax (CGT) exemption granted to homeowners when they sell their property.

However, Mr Warburton says that the rules that allow the self-employed to offset home running costs against tax are different to those that determine whether you have to pay any CGT on the property.

He says: “In the case of running costs, you can simply claim the proportion of your expenditure relating to the business, whether you use certain rooms for four days, five days or seven days.

“But when it comes to selling your home, you will lose your CGT exemption only on rooms that have been used exclusively for business purposes. In other words, if you use a room to carry out business five days a week and then let your children play in it for the other two, you would retain your CGT exemption on that room and not have to pay any tax when the property is sold.

“You could, however, claim your running costs against income tax. So those working from home can win on the swings while not losing on the roundabouts.”

Stephen Alambritis, of the Federation of Small Business, adds: “We reckon that about half of the 2.7 million self-employed people in the UK work wholly or partly from home, so these tax rules could affect about 1.35 million people - and the number is growing all the time.”